The invention relates generally to an electric valve actuation system.
Piston machines such as internal combustion engines, piston compressors, and expanders normally use valves for establishing proper gas exchange processes in the machine. The valves are typically driven directly or indirectly by cams provided on a camshaft. In piston compressors, these valves may be driven by pneumatic or hydraulic means, or the valves may open and close without actuators due to the differential pressure acting on the valves. In engines the cams open (lift) the valves for a certain amount of time (duration) during each intake and exhaust cycle. The camshaft is driven by a crankshaft through timing belts, gears, or chains, for example.
At higher engine speeds, an engine requires more air. If the intake valves close before the required amount of air flows into the cylinder, engine performance is reduced. If the cam keeps the valves open for longer periods of time, unburnt fuel will exit the engine and result in lower engine performance and increased emissions.
For piston machines such as engines and compressors, variable valve timing (VVT) has high potential to reduce emissions (for engines) and increase efficiency (for compressors and engines). Changing the opening and closing time of the valves of an engine in a dynamic way (cycle by cycle), the combustion process can be better controlled for different operation set points which leads to better overall engine performance (higher efficiency and less emissions). Active control of valve timing of piston compressor valves avoids flow-bypass arrangements and thus enables high efficient part load operation. Additionally, it enables the use of adapted valve shapes, which increases overall efficiency of the compressor due to reduced valve losses. High dynamic changes in gas delivery can be also achieved with this technology. It is advantageous that with such an actuation system, gas exchange in each cylinder can be individually controlled. The method can be used to turn on and off each cylinder individually leading to a more flexible machine, which delivers power (in case of an engine) or compressed gas (in case of a compressor) on demand at lower energy losses. In one example, mechanical actuation systems are used to actuate valves of the piston machine. However, a mechanical actuation system provides only limited variability in terms of valve timing. In another example, hydraulic systems are used to actuate valves of the piston machine. However hydraulic systems suffer from a large and costly infrastructure for the fluid and from limited reliability.
Accordingly, there is a need for a compact system that facilitates greater flexibility in valve timing.